1. Field of the Invention
The present invention relates to an alternator (an alternating current generator) for use in an automotive vehicle.
2. Description of Related Art
An engine compartment size is becoming smaller in a recent vehicle to employ a so-called slant-nose design and to secure a sufficient space for a passenger compartment. There is a tendency that temperature in the congested engine compartment becomes high. In addition, a higher output of an alternator is required to fulfill power consumption in various electric and electronic devices although an idling rotational speed of the alternator is becoming lower to improve fuel economy. Under these circumstances, it is unavoidable that a temperature rise in the alternator becomes higher, especially in a rectifier that converts alternating current to direct current. Therefore, it is required to efficiently cool the rectifier in a limited space.
Because of the slant-nose design, a possibility that water splashed by tires or foreign particles enter into the engine compartment becomes high. Especially in cold seasons, salt water for melting snow splashed by tires reaches the alternator. In addition, cleanser liquid used in a car-wash may reach and enter the alternator.
To enhance the efficiency in cooling the rectifier, JP-A-11-164538 proposes to provide a radial air passage to directly blow cooling air to a heatsink plate of a rectifier, which is located far from a usual cooling air inlet port. Further, JP-A-2001-169510 discloses a rectifier heatsink plate having cooling fins formed thereon and through-holes for introducing cooling air.
Though the radial air passage proposed by JP-A-11-164538 improves the cooling efficiency to a certain extent, the radial passage alone is not sufficient to cope with a temperature rise that is becoming higher and higher in recent high power alternators. It may be possible to further improve the cooling efficiency by enlarging the heatsink plate size. However, such a countermeasure is contradictory to a requirement for reducing the alternator size. Though the cooling fins proposed by JP-A-2001-169510 help improve the cooling efficiency, the cooling fins standing on a pair of heatsinks overlapping each other make the axial length of the rectifier longer. This is also against the requirement for down-sizing. In both of the prior publications referred to above, no countermeasure against the splash of water or cleanser liquid is provided or considered.